This invention relates to an improvement to evolutive codings utilizing a pseudo-random discontinuous function.
Electronic codings for security devices, especially for remote control, belong to one of three main groups:
1. Fixed codes.
2. Codes that vary according to a continuous law.
3. Codes that vary according to a discontinuous law.
The first two types of code suffer from the serious disadvantage of permitting relatively easy violation by recording of the signal transmitted for the first group and by recording several signals in order to deduce the law of variation for the second group.
The codes of the third type possess a much higher level of security, because the code changes after each use in accordance with a discontinuous mathematical function as a result of the generating pseudo-random numbers, this law being different for each transmitter-receiver assembly and being linked to a specific base code.
Nevertheless, such discontinuous mathematical functions which generate pseudo-random numbers are of necessity restricted functions that draw lots between a minimum and a maximum value. The maximum value may be deduced relatively easily according to the number of bits transmitted. Systematic scanning of all the values up to the maximum value will generally enable the security device to be unlocked.